Process for the production of cis-1,4-polyisoprene

ABSTRACT

In the process for producing cis-1,4-polyisoprene by polymerizing isoprene using a catalyst consisting essentially of an organoaluminum compound and a titanium tetrahalide, the improved process which comprises effecting the polymerization reaction in the presence in the polymerization system of ethylene in an amount not exceeding 8 parts by weight per 100 parts by weight of the isoprene.

United States Patent Hasegawa et al.

[15] 3,684,785 1451 Aug. 15, 1972 [72] Inventors: Hiroaki Hasegawa,Tokuyama; Kou- 3,476,721 11/1969 Binderetal. ..260/82.l

Primary Examiner-Joseph L. Schofer Assistant Examiner-Richard A. Gaither gg gf 2:22: Attorney-Sherman and Shalloway Moriguchi Yokohama, all of Japan [57] ABSTRACT Assigneci The Japanese p"?! -i In the process for producing cis-l,4-polyisoprene by Tokyo. Japan polymerizing isoprene using a catalyst consisting essentially of an organoaluminum compound and a [221 Sept' 1970 titanium tetrahalide, the improved process which com- [2l] Appl. No.: 72,367 prises effecting the polymerization reaction in the presence in the polymerization system of ethylene in U 8 Cl 260/85 3 260,94 3 an amount not exceeding 8 parts by weight per 100 c t b i t fth i rene. [51] Int. Cl ..C08d 1/14, C08d 1/36, C08d 3/10 p gh p [58] Field of Search ..260/94.3, 82.1, 85.3

[56] References Cited 6 Claims, 1 Drawing Figure UNITED STATES PATENTS 7 3,029,231 4/1962 Amerongennm'. ..260/87.5

EXAMPLE 7 (O 8 42b 25 r V) EXAMPLES ZOJ 37.0 I EXAMPLES CONTROL 3 .coNTRoL 2 o a'ao 1120 2'00 360 STRAIN (mm) PATENTEDMIQ 15 I972 EXAMPLE 7 EXAMPLE 6 CONTRO L 3 EXAMPLE 5 CONTROL 2 STRAIN 4 38: mwmEm PROCESS FOR THE PRODUCTION OF CIS l ,4-

. POLYISOPRENE This invention relates to a process for the production of cis-l,4-polyisoprene. More particularly, the invention relates to a process for producing cis-l ,4- polyisoprene wherein in polymerizing isoprene using a catalyst consisting essentially of an organoaluminum compound and a titanium tetrahalide the polymerization reaction is conducted in the presence of a small amount of ethylene not exceeding 8 parts by weight per 100 parts by weight of isoprene.

Numerous reports regarding the method of producing polyisoprene containing the cis-l ,4 configuration to a high degree have been made in the past. For example, it is well known that polyisoprene containing the cis-l ,4 configuration to a a high degree are formed by polymerizing isoprene using as the polymerization catalyst a suspension consisting of a trialkyl aluminum and titanium tetrachloride. The polyisoprene formed in this manner possesses properties which are such as to match natural rubber in many respects and thus is a very valuable elastomer for use as a general purpose rubber. On the other hand, there are such defects as that its unvulcanized rubber strength being low its processability is poor or that its modulus of elasticity is low. Various studies have been made for improving on these defects of cis-l,4polyisoprene. One, for example, was that wherein it was conceived to increase the molecular weight. For obtaining a polymer of high molecular weight, this can be done by changing the polymerization conditions. For instance, the degree of polymerization usually can be raised by either lowering the polymerization temperature or reducing the amount of the catalyst. However, while a change of one of the factors of the polymerization conditions in this manner doesbring about a desirable effect of increasing the molecular weight, on the other hand, undesirable results are concomitantly brought about. For example, when the polymerization temperature is lowered, the molecular weight rises but, on the other hand, since the polymerization speed is retarded, this becomes an exceeding disadvantage in the case where the operation is to be carried out commercially.

An object of the present invention is to provide a process for producing cis-l ,4-polyisoprene wherein this elastomer is improved in its unvulcanized rubber strength and modulus of elasticity without changing the polymerization conditions, as noted hereinabove.

Other objects and advantages of the invention will become apparent from the following description.

I found that a polyisoprene of high Mooney viscosity could be produced without bringing about any changes in the polymerization speed and cis-1,4 content, if the polymerization of isoprene is carried out in the presence of a small amount of ethylene. I found, moreover, that the so produced polyisoprene had an unvulcanized rubber strength which was greatly superior to that of the conventional polyisoprene, being even superior to natural rubber.

According to the invention process, the Mooney viscosity of the polyisoprene formed varies in accordance with the changes in the amount of ethylene that is added to isoprene, the Mooney viscosity increasing as the amount added of ethylene is increased, provided the other conditions are constant. While it was known heretofore to use the alpha-olefins as a molecular weight modifier in polymerizing butadiene, it was rather unexpected that by the addition of a small amount of ethylene in the case of the polymerization of isoprene the Mooney viscosity would increase. And moreover, a surprising fact is that. the addition of the alpha-olefins other than ethylene such, for example, as propylene, butene-l, isobutylene and styrene does not bring about an increase in the Mooney viscosity. Another interesting thing about the invention process is that the solution viscosity of the polymerization system demonstrates a pronounced drop as compared with the instance where the ethylene is absent. As a consequence, the heat removal from the polymerization system and its agitation is facilitated, thus making it easy to maintain the polymerization system in a uniform state.

Hence, cis-l,4-polyisoprene which has been improved in its unvulcanized rubber strength, a defect heretofore possessed by the polyisoprene rubber, as well as in its modulus of elasticity and tear strength is obtained when the invention process is followed. In addition, the drop in the solution viscosity of the polymerization system is surprising. For example, in the case of a pure rubber compound of polyisoprene formed by the presence of 2 parts by weight of ethylene per parts by weight of isoprene, the unvulcanized rubber strength and modulus at 300 percent are both more than twice that of the usual polyisoprene. Again, the solution viscosity drops to below one-fourth. Usually, oil extending is economically important in the case where polyisoprene is to be used in a heavy duty tire using natural rubber, but in this case usually a high Mooney viscosity is required in order to qualify for use as a base polymer for oil extending use. The use for this purpose of the high Mooney viscosity polymer obtained by the invention process is an exceeding advantage.

The accompany drawing illustrates the increase in the unvulcanized rubber strength of the polyisoprene obtained by the invention process. The numerals indicated along the several curves are the compounded Mooney viscosity (ML /l00 C.) of the several samples.

The amount present of ethylene according to the invention process is an amount less than 8 parts by weight, and preferably 1-5 parts by weight, per 100 parts by weight of isoprene. When the amount of ethylene exceeds 8 parts by weight, the product obtained loses its properties as an elastomer and becomes unsuitable for use as a general purpose rubber. The ethylene may usually be added in advance to the mixture of the monomer and solvent but need not necessarily be limited to such a procedure.

The catalyst used is a Ziegler catalyst consisting essentially of two classes of components at least one being selected from each of the two groups of (A) an organoaluminum compound of the formula Al m wherein R, is selected from the group consisting of hydrogen, halogen, alkyl, cycloalkyl, aryl and aralkyl,

R and R are selected from the group consisting of alkyl, cycloalkyl, aryl and aralkyl; and (B) titanium tetrahalides. Also useable is one which has also been incorporated with a Lewis base, such as an amine, or an unpolymerizable ether, as a third component.

The organoaluminum compounds, which are useable in the invention, include such, for example, as trialkylaluminums as triethylaluminum, triisobutylaluminum and trihexylaluminum; tricycloalkylaluminums as tricyclopentylaluminum and tricyclohexylaluminum; triarylaluminums as triphenylaluminum and tri(o-, mand p-tolyl) aluminum; triaralkylaluminums as tribenzylaluminum; and alkylaluminum halides as diethylaluminum chloride and other alkylaluminum compounds as diethylaluminum hydride.

The titanium tetrahalides, which are useable in the invention, include titanium tetrafluoride, titanium tetrachloride, titanium tetrabromide, titanium tetraiodide, and the mixtures thereof.

following non-limitative examples are given.

oh the other hand, the ethers capable of being used include the aliphatic ethers, aromatic ethers, aliphaticaromatic ether mixtures and the various types of cyclic ethers, examples beihg dimethyl ether, diethyl ether, di-n-butyl ether, diphenyl ether, anisole, styrene oxide, furan and tetrahydrofuran. Further, as the amines, useable optionally are the primary, secondary and tertiary amines of preferably not more than 18 carbon atoms such as methylamine, dimethylamine, trimethylarnine, diethylamine, triethylamine and tripropylamine; the primary, secondary and tertiary ally] and aralkyl amines such as phenylamine, diphenylamine, triphenylamine and tribenzylamine; alicyclic amines such as cyclohexylamine; and heterocyclic amines such as pyridine, N-ethylpyridine and pyrrole.

The polymerization reaction is preferably carried out in the presence of a solvent. The solvents used are usually the inert organic hydrocarbons such, for example, as the aliphatic hydrocarbons as n-butane, n-pentane, n-hexane and n-heptane; the alicyclic hydrocarbons as cyclohexane; the aromatic hydrocarbons as benzene and toluene; the saturated halogenated hydrocarbons as ethylene dichloride; and mixtures of two or more of the foregoing hydrocarbons.

The catalyst used in practicing the present invention is highly sensitive to oxygen and water. Since these are harmful to the catalytic activity, it is necessary to ensure that oxygen and water are fully removed from the monomer, inert solvent and ethylene. The polymerization reaction is carried out by the addition to the polymerization system of a catalyst suspension ob- EXAMPLES I-IY A 800-ml pressure bottle, after washing and drying, was thoroughly purged of its inside with nitrogen. This bottle was then charged with about grams of isoprene, about 270 grams of n-hexane and ethylene in a varied quantity as indicated in Table l. Separately, a ZOO-m] flask, after being washed, dried and thoroughly purged of its inside with nitrogen, was charged with ml of a n-hexane solution of titanium tetrachloride (concentration 1.43 mols/liter), followed by the addition of 26.5 ml of a n-hexane solution of triisobutylaluminum (concentration 3.78 mols/liter) and 20 millimols of di-n-butyl ether, whereupon a brown precipitate solution (molar ratio of Al Ti ether 1.0 1.0 0.2; titanium concentration 1.0 mol/liter) was obtained as the catalyst. This catalyst was added to the aforesaid pressure bottle with a syringe in amount corresponding to 7.5 millimols, calculated as titanium, per each mo] of the monomer, after which the polymerization reaction was carried out for one hour at a polymerization temperature of 30 C.

After completion of the polymerization reaction, the contents of the bottle was withdrawn and introduced into methanol containing 2 percent by weight of phenyl-beta-naphthylamine thereby solidifying the polymer, which was dried under vacuum for at least 12 hours at 70 C. The yield, gel content, Mooney viscosity, cement viscosity and content of cis-l,4 units were measured. The content of the cis-l,4 units was determined by means of infrared analysis. The gel content was measured in the following manner. 0.2 Gram of the polymer was placed in an -mesh wire gauze and dissolved for 24 hours with toluene. The portion remaining undissolved after this treatment was measured and this was designated the gel content. On the other hand, the cement viscosity was measured at the time of the completion of the polymerization reaction, using a Model B viscometer. The results obtained are shown in Table 1.

TABLE 1 Ethylene Mooney to Ucl Cis-l ,4 viscosity Cement Experiment lsopren irllexune Ethylene isoprene Yield content content M lw/ viscosity Number (g.) (g.) (g ratio" (percent) (percent) (percent) C. (G?) Control 1 60 Z70 47.2 0. 8 J8. 4 04.0 .I 500 Example I 60 270 0. 42 0. T 45. 2 l3. 0 025. 4 100. 0 3, 500 Example II 60 270 1.20 2. 0 50. 4 219.5 02$. 3 106. 0 l, 000 Example Ill 60 270 2.80 4. T 45.0 43.0 025.3 114.0 1,000 60 270 4. 80 8. 0 46. 0 65. 4 H8. 4 120. 0 500 Example I\' Parts by weight of ethylene per 100 parts by weight of isoprt-x tained by mixing the tianium tetrahalide and the organoaluminum compound in the prescribed amounts (to which may also be added as a third component a 65 Lewis base). In this case the proportion in which the titanium tetrahalide and organoaluminum compound are used is suitably a molar ratio of Al/Ti 0.5 3.0,

EXAMPLES V-VIII Ethylene in a varied quantity as indicated in Table 2 was added to 100 parts by weight of isoprene, the polymerization reaction being otherwise carried out as in Examples l-IV. The resulting polyisoprene, after being compounded in accordance with the following :recipe, was tested for its properties.

Parts by Weight Polyisoprene I Stearic acid Zinc oxide Sulfur Calcium carbonate Titanium dioxide Diphenyl guanidine l-lexamethylenetetramine Styrenated phenol The polymer of Control 11 is the polymer obtained in Control I. On the other hand, the polymer of Control 111 was obtained by changing the amount of the catalyst to an amount corresponding to 4.0 millimols, calculated as titanium, per each mol of the monomer, and carrying out the polymerization reaction for 8 hours at a temperature of 0 C. The tensile strength, elongation, modulus at 300 percent, tear strength and unvulcanized rubber strength were measured in accordance with JIS K 63011962. In the tear strength test a JIS-A type piece was used( as the specimen, while a dumbbell specimen No. 3 of a dimension 20 X 5 X 2 mm was used in measuring the unvulcanized rubber strength. The results obtained are shown in Table 2 and the accompanying drawing.

1n the case of the Control IV polyisoprene in which the amount incorporated of the ethylene was parts by weight, the compounded Mooney viscosity was excessive and no matter how the amounts of the compounding agents were changed, no great drop in this value could be achieved. Hence, it is clear that polyisoprene of this sort cannot be used as a general purpose rubber.

TABLE 3 Alpha- Mooney Control alpha- Olefin to Yield Gel Cis-l ,4 viscosity Experiolefin lsoprene content content ML J ment used Ratio 100C.

V 47.2 6.8 98.4 94.0 V1 propylene 5.0 40.3 5.5 98.2 92.0 V11 butene-l 5.0 45.0 4.5 98.4 85.0 V111 isobutylene 5.0 45.8 4.0 98.3 86.0 1X styrene 5.0 42.0 4.9 98.9 90.0

"Parts by weight of alpha-olefin per 100 parts by weight of isoprene.

We claim:

1. In the process for producing cis-1,4-polyisoprene by polymerizing isoprene using a catalyst consisting essentially of an organoaluminum compound of the formula ceeding 8 parts by weight per 100 parts by weight of the isoprene.

2. The process of claim 1 wherein the molar ratio of titanium to aluminum in said catalyst is 1:0.5-1:3.0.

Tail 1E 2 COm- Unvnlcan- Polymer pounded izoil rnblwr- Arnount Mooney Mooney Tensile strength Elongation Modulus at 300% Tear strength strength, added of viscosity, viscosity, (kg/cm?) (percent) (kg/cm?) (kg/cm?) (kg/cm?) Experiment ethylene MIi+i/- M1|+.'/- (maximum number (wt. part) 100 C. 100 C. 30 min. min. 301n1n. 40111111. 30 n1in. 40 min. 30 min. 40 n1in. stress) Control II 0 94. 0 28. 0 188 171 730 730 2 23 20 30 l. 5 Control III 0 110.0 42. 0 105 181 720 720 27 28 30 3'2 3. 5 Example V 1. 5 104. 0 37. 0 195 103 690 600 30 30 2 33 5. 3 Example VI 2. 6 109. 5 42. 0 187 174 560 560 81 76 -17 52 33. 0 Example VII 5. 0 115. 0 45. 0 175 150 500 510 120 118 55 57 65. 0 Control IV 10, 0 125. 0 80. 0 110 05 70 65 1 70 1 vulcanization time.

CONTROLS v IX 3. The process of claim 1 wherein said catalyst 15 used in an amount that the titanium tetrahalide is present in an amount of 0.1-20 millimols per mol of isoprene.

4. The process of claim 1 wherein the polymerization reaction is carried out at a temperature ranging between -5 and C. i

5. The process of claim 1 wherein the polymerization reaction is carried out in an inert hydrocarbon solvent.

6. The process of claim 5 wherein the isoprene concentration in the solvent is 10 40 percent by weight. 

2. The process of claim 1 wherein the molar ratio of titanium to aluminum in said catalyst is 1:0.5-1:3.0.
 3. The process of claim 1 wherein said catalyst is used in an amount that the titanium tetrahalide is present in an amount of 0.1-20 millimols per mol of isoprene.
 4. The process of claim 1 wherein the polymerization reaction is carried out at a temperature ranging between -5* and 70* C.
 5. The process of claim 1 wherein the polymerization reaction is carried out in an inert hydrocarbon solvent.
 6. The process of claim 5 wherein the isoprene concentration in the solvent is 10 - 40 percent by weight. 